Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
  • H04N19/186—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being a colour or a chrominance component
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/70—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals characterised by syntax aspects related to video coding, e.g. related to compression standards

Definitions

• the present invention relates to the field of video compression and, for instance, more specifically to the video standards of the MPEG family (MPEG-1, MPEG-2, MPEG-4) and of the ITU-H.26X family (H.261, H.263 and extensions, H.26L).
• Said invention concerns a video coding method applied to a sequence of video frames and generating a coded bitstream in which each data item is described by means of a bitstream syntax allowing any decoder to recognize and decode all the segments of the content of said bitstream, each of said frames consisting of three rectangular matrices that are a luminance matrix and two chrominance ones.
• the invention also relates to a device for carrying out said coding method, to a transmittable video signal delivered by such a coding device, to a video decoding method for decoding said transmittable signal, and to a corresponding decoding device.
• each of the two chrominance channels contains a digital signal equal to a value comprised in the range defined by a chrominance representation on a given amount M of bits (eight bits for instance : with such a representation on eight bits, the values of the signal may vary between 0 and 255).
• each of the chrominance channels contains a flat signal equal to a constant value 2 M_1 .
• dct_dc_size_chrominance a variable length code, called dct_dc_size_chrominance, is used as a descriptive element encoding the size of the differential value that should be read from the transmitted or stored bitstream in order to update in the blocks of all intra macroblocks the last decoded chrominance DC coefficient and therefore obtain its current value.
• This differential value equal to 0 when the chrominance signal is a constant value, is then encoded as "there is no differential value to be read" (i.e.
• CBP Coded Block Pattern
• This CBP element is then further encoded by variable length codes : the luminance and chrominance block patterns are jointly entropy-coded using a VLC table optimized for coloured sequences.
• this table is not optimized for black and white sequences : only 16 CBP values out of 48 are actually used, and the shortest VLC words are reserved for CBP values that are never encountered. It is difficult to precisely quantify this waste of bits, but it obviously exists.
• the invention relates to a method such as defined in the introductory part of the description and which is moreover characterized in that said syntax comprises a flag indicating at a high description level the presence, or not, of chrominance components, and to a corresponding coding device.
• the invention also relates to a transmittable video signal consisting of a coded bitstream generated by such a video coding method and in which each data item is described by means of a bitstream syntax allowing any decoder to recognize and decode all the segments of the content of said bitstream, each of said frames consisting of three rectangular matrices - a luminance one and two clrominance ones, said signal being characterized in that it comprises a syntactic element provided for indicating at a high description level the presence, or not, of chrominance components, and to a video decoder for receiving and decoding such a video signal.
• the invention also relates to a video decoding method for decoding said transmittable video signal, and to a corresponding decoding device.
• Fig.1 shows an example of an MPEG coder with motion compensated interframe prediction.
• a syntactic element is defined, such as, in the present case :
• Video_object_layer_chrom and the semantic meaning of this element is : "this is a one bit flag indicating, if set to a given value (for example, one), that the chrominance channel is present and should be decoded, and, if not, that both chrominance channels are set to the relevant monochrome constant value".
• This technical solution is particularly advantageous, since it noticeably reduces the waste of bits by using means that are neither contemplated nor suggested in the standards. It must indeed be noted, for example in the MPEG-4 syntax, that there is also, in the document w3056 cited above, another syntactic element related to the chrominance, called "chroma_format” and given at the VOL level.
• the video coding method described above may be implemented in a coding device such as for instance the one illustrated in Fig.1 showing an example of an MPEG coder with motion compensated interframe prediction, said coder comprising coding and prediction stages.
• the coding stage itself comprises a mode decision circuit 11 (for determining the selection of a coding mode I, P or B as defined in MPEG), a DCT circuit 12, a quantization circuit 13, a variable-length coding circuit 14, a buffer 15 and a rate control circuit 16.
• the prediction stage comprises a motion estimation circuit 21, a motion compensation circuit 22, an inverse quantization circuit 23, an inverse DCT circuit 24, an adder 25, and a subtracter 26 for sending towards the coding stage the difference between the input signal IS of the coding device and the predicted signal available at the output of the prediction stage (i.e. at the output of the motion compensation circuit 22).
• This difference is the bitstream that is coded
• the output signal CB of the buffer 15 is the coded bitstream that, according to the invention, will include the one bit flag indicating that the chrominance is, or not, present in the input signal and will have, or not, to be decoded at the decoding side.
• each scene which may consist of one or several video objects (and possibly their enhancement layers), is structured as a composition of these objects, called Video Objects (VOs) and coded using separate elementary bitstreams.
• the input video information is therefore first split into Video Objects by means of a segmentation circuit, and these VOs are sent to a basic coding structure that involves shape coding, motion coding and texture coding.
• Each VO is, in view of these coding steps, divided into macroblocks, that consist for example in four luminance blocks and two chrominance blocks for the format 4:2:0 for example, and are encoded one by one.
• the multiplexed bitstream including the coded signals resulting from said coding steps will include the one bit flag indicating that the chrominance is, or not, present in the input signal and will have, or not, to be decoded at the decoding side.
• this flag transmitted to the decoding side, is read by appropriate means in a video decoder receiving the coded bitstream that includes said flag.
• the decoder which is able to recognize and decode all the segments of the content of the coded bitstream, reads said additional syntactic information and knows that the chrominance channel is, or not, present and has therefore to be decoded, or not.
• Such a decoder may be of any MPEG- type, as the encoding device, and its essential elements are for instance, in series, an input buffer receiving the coded bitstream, a VLC decoder, an inverse quantizing circuit and an inverse DCT circuit. Both in the coding and decoding device, a controller may be provided for managing the steps of the coding or decoding operations.
• the coding and decoding devices described herein can be implemented in hardware, software, or a combination of hardware and software, without excluding that a single item of hardware or software can carry out several functions or that an assembly of items of hardware and software or both carry out a single function.
• the described method and devices may be implemented by any type of computer system or other adapted apparatus.
• a typical combination of hardware and software could be a general-purpose computer system with a computer program that, when loaded and executed, controls the computer system such that it carries out the method described herein.
• a specific use computer, containing specialized hardware for carrying out one or more of the functional tasks of the invention could be utilized.
• the present invention can also be embedded in a computer program product, which comprises all the features enabling the implementation of the method and functions described herein and -when loaded in a computer system- is able to carry out these method and functions.
• Computer program, software program, program, program product, or software in the present context mean any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following : (a) conversion to another language, code or notation ; and/or (b) reproduction in a different material form.

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• 2002
  • 2002-07-18 WO PCT/IB2002/003130 patent/WO2003013147A1/en active Application Filing
  • 2002-07-18 KR KR1020047001642A patent/KR100941641B1/ko active IP Right Grant
  • 2002-07-18 CN CNB02815052XA patent/CN100380983C/zh not_active Expired - Lifetime
  • 2002-07-18 JP JP2003518189A patent/JP2004537932A/ja active Pending
  • 2002-07-18 EP EP02751546A patent/EP1415479A1/en not_active Ceased
  • 2002-07-30 US US10/208,361 patent/US8548050B2/en active Active

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